All mine are fed Naturediet, Minstrel and Branston have lamb & rice, they have approx 200grams 3 times per day (equiv. to 1.5 trays each), which along with various biscuit treats during the day they seem to do well on. I know the feeding guide for the fish one is quite a lot more, and can only imagine it is because fish itself is quite light.
I expect you saw my reply on the other thread about them bringing out some grain-free food and also some dry, but it seems very much a wait and see thing, in regard to what and when will definitely be available.
Why not go on their Facebook page and send them a private message, saying you have heard rumours about new lines and see what they come up with?